The primary goal of these studies is to understand the regulation of intracellular calcium in mammalian central neurons following activation by excitatory amino acids, especially through the NMDA receptor. Elevation of calcium via glutamate receptor activation has been implicated in regulation of long term potentiation in mammalian hippocampal pyramidal neurons, generation of rythmic pacemaker-like activity which may control pattern generation in efferent motor systems, as well as the excitotoxic action of some excitatory amino acid agonists. The three sources of calcium that may contribute to the elevation of intracellular calcium following activation are through voltage- dependent calcium channels, glutamate-gated channels, or glutamate activation of intracellular release of calcium. By combining the use of electrophysiological techniques and optical recording of intracellular calcium through the use of calcium- sensitive dyes, it will be possible to determine the conditions under which each source contributes optimally to elevation of intracellular calcium. It will also be possible to measure and manipulate the kinetics of recovery from agonist-induced calcium loads in order to help identify the mechanisms which contribute to calcium clearance. Finally, the physiological consequences of glutamate-induced elevation of intracellular calcium will also be studied including possible activation of calcium-dependent potassium, chloride, and other cation channels. The experiments in this proposal will provide new, direct information on a previously incompletely described component of the response to glutamate; elevation of intracellular calcium.